1. FIELD OF THE INVENTION
The present invention relates to a chip type of noise suppressing filter for suppressing noise electromagnetically generated in signal lines or electric source lines of an electronic apparatus, and a method for manufacturing the noise suppressing filter.
2. DESCRIPTION OF THE RELATED ART
A chip type of noise suppressing filter has been manufactured to suppress noise electromagnetically generated in signal lines or electric source lines of an electronic apparatus.
FIG. 1 is an exploded and diagonal view of a conventional noise suppressing filter.
As shown in FIG. 1, a conventional noise suppressing filter 11 comprises a chip capacitor 12 for holding electric charges, and a U-shaped ferrite core 13 having a hollow portion 13a. The chip capacitor 12 is put in the hollow portion 13a of the ferrite core 13. The ferrite core 13 is provided with a pair of through holes which each penetrate the ferrite core 13 from the hollow portion 13a thereof to an outside thereof and a pair of through-hole conductors 14 put in the through-holes. Each of the through-hole conductors 14 functions as an induction coil.
The filter 11 further comprises a pair of external electrodes 15 which each are attached to a side surface of the ferrite core 13, and an intermediate electrode 16 put in the hollow portion 13a of the ferrite core 13. Each of the external electrodes 15 is provided for one of the through-hole conductors 14 to be electrically connected with an external line. The intermediate electrode 16 is provided for the chip capacitor 12 to be electrically connected with another external line.
Also, the chip capacitor 12 put in the ferrite core 13 is provided with a pair of electrodes 12a at both ends thereof. One of the electrodes 12a is electrically connected with the-intermediate electrode 16 through a piece of conductor 17. Another electrode 12a is electrically connected with the through-hole conductors 14 through a piece of conductor 18 which is put between the electrode 12a and surfaces of the through-hole conductors 14 exposed to the hollow portion 13a of the ferrite core 13.
FIG. 2 is an equivalent circuit of the conventional noise suppressing filter 11 shown in FIG. 1.
In the above configuration, as is well known, the conventional noise suppressing filter 11 in which one of the through-hole conductors 14, the chip capacitor 12 and another through-hole conductor 14 is arranged in series in that order suppresses noise electromagnetically generated in signal lines or electric source lines of an electronic apparatus which is connected with the conventional noise suppressing filter 11 through the external lines.
Next, a conventional method for manufacturing the conventional noise suppressing filter 11 is described.
The external electrodes 15, the intermediate electrode 16, and the conductors 17, 18 are produced by printing silver paste on the ferrite core 13 so that a film type of wiring network is produced on the ferrite core 13. In this case, the thickness of the external electrodes 15 and the intermediate electrode 16 ranges from several tens .mu.m to several hundreds .mu.m.
Also, the through-hole conductors 14 are produced by pouring the silver paste into the through-holes of the ferrite core 13.
However, because the external electrodes 15 and the intermediate electrode 16 are formed of the film type of wiring network, the external electrodes 15 and the intermediate electrode 16 are melted and cut out when a comparatively large intensity of electric current flows through the external electrodes 15 and the intermediate electrode 16. Therefore, the intensity of the electric current flowing through the conventional noise suppressing filter 11 is limited to a comparatively small value. As a result, in cases where a comparatively large intensity of electric current flows through an electronic circuit such as an electric source circuit, noise generated in the electronic circuit can not be suppressed by the conventional noise suppressing filter 11 because the electric current having the comparatively large intensity can not flow through the conventional noise suppressing filter 11.
Also, the silver paste must be poured into the through holes provided in the ferrite core 13 to produce the through-hole conductors 14. In addition, the silver paste must be printed several times to produce the external electrodes 15 and the intermediate electrode 16 while rotating the ferrite core 13, and the silver paste printed must be dried each time the silver paste is printed on a surface of the ferrite core 13. The silver paste is generally printed on five surfaces of the ferrite core 13.
Therefore, the manufacture of the conventional noise suppressing filter 11 becomes complicated.
In addition, when the silver paste is poured into the through holes to produce the through-hole conductor 14, the silver paste is leaked out from the through holes. Therefore, the through-hole conductors 14 are incompletely and unevenly solidified in the through holes. As a result, inductance of the through-hole conductor 14 can not be set to a regular value. Accordingly, there is a drawback that the conventional noise suppressing filter 11 having a regular value of inductance can not be reliably manufactured.